This Program Project Grant application, jointly submitted by the investigators at The University of Alabama at Birmingham and the University of Chicago, proposes to utilize novel and unique engineering of herpes simplex virus (HSV) in order to develop therapeutics of human gliomas. Novel approaches to the development of these constructs will utilize double labeled probes including Green Fluorescent Protein and beta-galactosidase (lacZ) in order to distinguish between latent and actively replicating virus in the central nervous system of treated animals. The development of these viruses will include novel foreign gene inserts to enhance the oncolytic activity of these viruses. Viruses generated in the first Project will have their biologic behavior evaluated in the second Project. These studies will include not only the assessment of survival but detailed evaluation of the central nervous system of treated scid or C57BL/6 mice bearing intracranial gliomas. The contribution of host immune responses to the oncolytic activity of these viruses will be evaluated. In parallel, studies in a flank glioma model in nude mice will be performed to determine whether the oncolytic effect of these genetically engineered HSV constructs is potentiated when used as radiation sensitizing agents in combination with radiotherapy. Tissue sections will be evaluated in the Experimental Glioma Tissue Core. We will test selected genetically engineered HSV constructs for neurovirulence in the HSV-sensitive simian primate, Aotus, in preparation for human clinical trials.